1. Field of the Invention
The present invention relates to a coma aberration correcting apparatus for an optical pickup, and more particularly, to a coma aberration correcting apparatus for an optical pickup, including an optical pickup main body having a photo diode, and an actuator mounted on an objective lens focusing a beam emitted from the photo diode.
2. Description of the Related Art
Generally, an optical pickup reads or writes data on a recording medium, such as a CD (compact disk) in an optical device, such as a CD-ROM (compact disk read only memory) drive, a CD-RW (compact disk rewritable) drive, a DVD (digital versatile disk) drive, etc.
The optical pickup includes an optical pickup main body having a photo diode emitting a laser beam, and an actuator mounted on an objective lens to focus the laser beam emitted from the photo diode onto the recording medium.
If the objective lens is mounted onto the optical pickup main body in an inclined state or in a wrong position, the beam emitted from the photo diode is not properly focused onto the recording medium, making it impossible to read or write data on the recording medium. Further, a coma aberration is one of the chief causes that makes the objective lens to not focus the laser beam from the photo diode onto the recording medium.
The coma aberration causes the laser beam emitted from the photo diode to not be focused at a point and looks like a comet-shaped image when the laser beam goes through the objective lens off from an optical axis at an angle.
Therefore, in order to focus the laser beam emitted from the photo diode onto the recording medium, there has been proposed a device to reduce the coma aberration when the objective lens is mounted onto the optical pickup main body.
FIGS. 1 and 2 are perspective views of a conventional coma aberration correcting apparatus for the optical pickup. As shown in FIGS. 1 and 2, the coma aberration correcting apparatus 101 includes a main base 103 to be seated on a plane, such as a table, a main supporting unit 120 detachably supporting an optical pickup main body 151 of an optical pickup 150 (to be described later), a holding unit 130 holding and releasing an actuator 153 put on the optical pickup main body 151 supported by the main supporting unit 120, an optical system 140 magnifying and photographing a laser beam emitted from a photo diode (not shown) through an objective lens 155 of the actuator 153 held by the holding unit 130, and a driving part 110 adjusting a position of the actuator 153 relative to the optical pickup main body 151.
As shown in FIG. 2, the optical pickup 150 includes the optical pickup main body 151 having the photo diode emitting the laser beam, and the actuator 153 mounted on the objective lens 155 focusing the laser beam emitted from the photo diode onto a recording medium (not shown), such as a CD.
The optical pickup main body 151 is firmly supported by the main supporting unit 120, and includes a pair of projections 157 to be combined with the actuator 153 in a state where the optical pickup main body 151 is supported by the main supporting unit 120, and a through hole 158 through which the holding unit 130 passes so as to hold the actuator 153 from below.
The actuator 153 is mounted on the objective lens 155 focusing the laser beam onto the recording medium, and is combined with the projections 157 of the optical pickup main body 151 by soldering after the position of the actuator 153 is adjusted by the coma aberration correcting apparatus 101 to correct the coma aberration of the objective lens 155. Herein, the actuator 153 is made of a magnetizable material so as to be attached to a holding part 131 of the holding unit 130 by a magnetic force.
As shown in FIG. 2, the main supporting unit 120 includes a main supporting base 121 shaped like a plate, a base supporter 122 (FIG. 1) having an upper part combined to the main supporting base 121 and a lower part combined to the main base 103 to support the main supporting base 121. The main supporting unit 120 also includes a main body supporter 128 combined onto the main supporting base 121 to support a first part of the optical pickup main body 151, a first cylinder 123 combined with the main supporting base 121 at a predetermined distance from the main body supporter 128 in a side opposite to the main body supporter 128, a slider 125 combined with the first cylinder 123 by a shaft 127 and sliding along a guide 126, and a jig 129 combined with the slider 125 and supporting a second part of the optical pickup main body 151.
The main supporting base 121 is formed with a base through hole 124 through which the holding unit 130 passes to hold the actuator 153 of the optical pickup 150.
The holding unit 130 is provided under the main supporting unit 120, and holds a lower part of the actuator 153. The holding unit 130 includes the holding part 131 holding the actuator 153 by the magnetic force, and a cylinder unit 133 provided adjacent to the holding part 131 to control the magnetic force of the holding part 131.
The holding part 131 is shaped like a bar, and has an upper part passing through the through hole 158 of the optical pickup main body 151 and holds the lower part of the actuator 153 by the magnetic force.
The cylinder unit 133 includes a pinion 138 rotating to control the magnetic force of the holding part 131, a rack 137 engaging to the pinion 138, and a second cylinder 135 provided adjacent to the rack 137 and reciprocating the rack 137 linearly.
Thus, in the holding unit 130, the rack 137 is linearly reciprocated according to an operation of the second cylinder 135. The pinion 138 rotates according to the reciprocating motion of the rack 137 and controls the magnetic force of the holding part 131, thereby allowing the holding part 131 to hold and release the actuator 153.
The optical system 140 includes a low magnification camera 141 and a high magnification camera 143 magnifying and photographing the laser beam emitted from the photo diode through the objective lens 155 of the actuator 153 held on the optical pickup main body 151 by the holding unit 130. The optical system 140 also includes a low magnification monitor 145 and a high magnification monitor 146 respectively displaying pictures transmitted from the low magnification camera 141 and the high magnification camera 143, respectively.
The low magnification camera 141 and the low magnification monitor 145 are generally used to schematically adjust a position of the laser beam emitted from the photo diode through the objective lens 155.
The high magnification camera 143 and the high magnification monitor 146 are generally used to correct the coma aberration of the laser beam emitted from the photo diode through the objective lens 155.
The driving part 110 is provided under the holding unit 130 and is used to adjust the position of the actuator 153, which is held on the optical pickup main body 151 by the holding unit 130, relative to the optical pickup main body 151. As a result, a position of the objective lens 155 mounted to the actuator 153 is adjusted. The driving part 110 includes an X-axis handle 111 and a Y-axis handle 113 to move the actuator 153 horizontally, a Z-axis handle 115 to move the actuator 153 vertically, and an R-axis handle 117 and a T-axis handle 119 to adjust an inclination of the actuator 153.
With the configuration described for FIGS. 1 and 2, the conventional coma aberration correcting apparatus 101 of the optical pickup 150 operates as follows.
First, the optical pickup main body 151 of the optical pickup 150 is placed on the main supporting unit 120 and is firmly supported according to an operation of the first cylinder 123. Then, the actuator 153 mounted on the objective lens 155 is put on the optical pickup main body 151 and the lower part of the actuator 153 is held by the holding part 131 according to an operation of the second cylinder 135 of the holding unit 130.
Then, a worker controls the X- and Y-axis handles 111 and 113 until the laser beam emitted from the photo diode through the objective lens 155 of the actuator 153 is displayed on the low magnification monitor 145 to display a picture photographed by the low magnification camera 141. When the beam from the photo diode is displayed on the low magnification monitor 145, the worker controls the X-, Y- and Z-axis handles 111, 113 and 115 so as to adjust a focus and a position of the laser beam from the photo diode. Further, in order to finely adjust the focus and the position of the laser beam from the photo diode, the worker controls the X-, Y- and Z-axis handles 111, 113 and 115, monitoring the laser beam photographed by the high magnification camera 143 and displayed on the high magnification monitor 146. Thereafter, the worker controls the R- and T-axis handles 117 and 119, monitoring the high magnification monitor 146, thereby correcting the coma aberration. Then, the actuator 153 is adjusted in a position to be combined with the pair of projections 157 of the optical pickup main body 151 by soldering.
Thus, in the conventional coma aberration correcting apparatus 101 for the optical pickup 150, the position of the objective lens 155 mounted to the actuator 153 is adjusted by adjusting the position of the actuator 153 relative to the optical pickup main body 151, thereby correcting the coma aberration of the optical pickup 150.
However, in the conventional coma aberration correcting apparatus 101 for the optical pickup 150, the worker must manually control the driving part 110 so as to combine the actuator 153 having the objective lens 155 with the optical pickup main body 151 without the coma aberration. As a result, the optical pickup 150 cannot be uniformly manufactured and productivity thereof is decreased. Particularly, correcting the coma aberration of the optical pickup 150 requires fine adjustment, creating a need for skilled workers.